The present invention relates to a scheduling apparatus, a scheduling method and a communication control apparatus, and more particularly, to a scheduling apparatus, a scheduling method and a communication control apparatus used for cell transmission scheduling or cell transmission shaping of a network apparatus such as asynchronous transfer mode (ATM) or the like.
A conventional scheduling apparatus, a scheduling method and a communication control apparatus of this kind has a shaper for holding the execution time of events corresponding to the events. To obtain an event to be executed at the current time, all shapers are investigated and an event with an execution time coinciding with the current time is selected. In an apparatus such as ATM, or the like, it is necessary that a single physical line be handled as a large amount of virtual lines of 60,000, or the like, that different cell rates are set to the respective lines and that the cell rate covers a wide range of 1 through 232 cells per second, or the like. However, in the conventional apparatus and method, all of the shapers must be investigated in order to obtain an event executed at the current time. Therefore, a problem is created because the processing time period increases when the cell rate and capacity of the shaper increase.
An example of a scheduling apparatus addressing this problem is disclosed in EPO782303. According to the scheduling apparatus described in the publication, a time slot is provided for holding an identifier of an event corresponding to the event execution time. The apparatus schedules cell by reading out the time slot at a constant time interval. More specifically, in the apparatus and method described in the publication, the time information obtained is a multiple of a predetermined minimum time interval, is represented by binary integer data, and is used for writing to and reading from a time slot. However, a problem occurs because the capacity of a memory constituting the time slot becomes large when a wide range of communication rates are required in the apparatus, such as ATM.
Also, anther problem is created because it is inefficient to schedule the event based on time information obtained from a multiple of a predetermined minimum time interval for an event in which a highly accurate execution time is not required.
An object of the present invention is to provide a scheduling apparatus, a scheduling method and a communication control apparatus which can efficiently handle a wide range of communication rates.
Another object of the present invention is to provide a scheduling apparatus, a scheduling method and a communication control apparatus in which a scheduling table requires less memory than the conventional apparatus or method.
According to one aspect of the present invention, a scheduling apparatus is provided which includes: a first element which stores a data pair comprised of (1) an identifier for identifying a communication event and (2) time information which shows time for executing the communication event and is represented by floating point data having an accuracy necessary for the communication event; and a second element which reads out the identifier from the first element by using, current time information which is represented by the floating point data.
According to another aspect of the present invention, a scheduling apparatus is provided which includes: a first element which stores a data pair comprised of (1) a first event to be executed at a first execution frequency and (2) first time information which has a first accuracy based on the first execution frequency and shows the time when the first event is executed; and stores a data pair comprised of (1) a second event to be executed at a second execution frequency and (2) second time information which has a second accuracy based on the second execution frequency and shows the time when the second event is executed; and a second element which converts current time to either of the first or second time information; and a third element which reads out the first event or the second event stored in the first element by using the first time information or the second time information converted from the current time by the second element.
According to another aspect of the present invention, a scheduling method, which is performed by an apparatus connected to a storing element, is provided which includes: storing a data pair comprised of (1) an identifier that identifies a communication event and (2) time information which shows the time for executing the communication event and is represented by floating point data having an accuracy necessary for communicating the communication event to said storing element; and reading out the identifier from the storing element by using current time information which is represented by the floating point data.
According to another aspect of the present invention, a communication control apparatus is provided which includes: a first element which outputs time information which shows the time of executing a communication event and is represented as floating point data having an accuracy necessary for communicating the communication event and outputs an identifier which identifies the communication event corresponding to the time information; a second element which receives the time information and the identifier from the first element and stores a data pair comprised of (1) the time information and (2) the identifier; and a third element which reads out the identifier from the second element by using current time information which is represented by the floating point data.